1. Field of the Invention
The present invention relates to a semiconductor device. In particular, the present invention relates to a semiconductor device whose operation mode is switchable.
2. Description of Related Art
A technique that selectively activates a desired function in a semiconductor device is known. For example, differently specified circuits are beforehand installed in the same semiconductor chip in order to support different specifications of users. The same semiconductor chip can provide individual function required by each user by switching an operation mode.
As a related technique, U.S. Pat. No. 5,754,879 discloses a technique that performs mode switching by using existing specific terminals (pads) such as a VDD terminal (power-supply terminal), a GND terminal (ground terminal) and a RESET terminal (reset terminal). According to the related technique, no special external terminal is necessary. However, it is required to design the three pads to be connectable to the same external terminal. In this case, in order to avoid problems such as intersection of interconnections, it is necessary to collectively place the three pads dedicated to the mode switching. Moreover, the three pads each cannot be used as an input/output pad.
Japanese Laid-Open Patent Application JP-2004-047720 discloses a technique that switches two operation modes by changing wire bonding to a package pin. According to this related technique, one of two pads can be used for the operation mode switching and the other can be used as an input/output pad, by the operation mode switching. According to this related technique, however, a level of an input signal input to the pin is changed when the mode is switched. That is, it is necessary to prepare a special input signal when performing the mode switching.
The inventor of the present application has recognized the following points.
In general, an operation mode switch pad is arranged close to the specific terminals such as the RESET terminal (reset terminal) and the VDD terminal (power-supply terminal). However, it is not possible to arrange a lot of operation mode switch pads near the specific terminals, due to layout restriction. Moreover, the semiconductor device is increasingly miniaturized in recent years. As the miniaturization proceeds, the number of internal circuits that can be arranged increases and thus increase in the number of pads is required. However, a pad size and arrangement-permitted areas are predetermined, due to precision of bonding and the like. Thus, even when the miniaturization of the semiconductor device proceeds, degree of freedom of the pad arrangement is not so improved. Therefore, an operation mode switching technique is important. However, according to the existing operation mode switching technique, it is required to prepare a plurality of dedicated pads or a special external environment in order to switch the operation mode of the semiconductor device.